The Supercharged-and-Intercooled Free-Piston-and-Turbine Compound Engine—A Cycle Analysis

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Abstract
This paper supplements a previous study. Its purpose is to clarify the position occupied by the supercharged-and-intercooled cycle variant of the free-piston-and-turbine compound engine relative to the simple cycle. Two points of view are employed in these considerations—one relating to question of whether or not to supercharge an existing simple-cycle prototype; and the second relating to the basic decision of whether to develop a supercharged-and-intercooled cycle, or alternatively to develop the simple cycle for the same degree of pressure charging of the engine cylinder. From the first viewpoint, as an example, it appears to be attractive to supercharge a 6:1 pressure-ratio simple cycle up to 8:1 by a blower of 1.33 pressure ratio. The gain is roughly 50 per cent in power output and this must be weighed against the additional complexity, bulk, weight, and cost associated with the supercharger and its turbine drive, together with the intercooler and its ducting. Moreover, the cylinder combustion rate is increased in proportion to the power gain so that cylinder and piston heat problems are more severe. From the second viewpoint, the supercharged-and-intercooled cycle possesses no significant advantages and many disadvantages.

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